When is it appropriate to order an antinuclear antibody IgG enzyme-linked immunosorbent assay (ANA IgG ELISA)?

When to Order ANA IgG ELISA

ANA IgG ELISA should NOT be used as a first-line screening test for systemic autoimmune rheumatic diseases (SARD); indirect immunofluorescence assay (IIFA) on HEp-2 cells remains the reference standard for ANA screening. 1

Primary Screening Approach

The international consensus is clear: IIFA is the reference method for ANA screening 1. Alternative assays like ELISA can be used, but with critical caveats:

• If clinical suspicion is strong and ELISA is negative, you MUST perform IIFA 1
• Tests based on restricted mixtures of defined nuclear antigens (like many ELISAs) should not be referred to as "ANA test" or "ANA screen" 1

When ANA IgG ELISA May Be Appropriate

1. As a Reflex Test After Positive IIFA

Following a positive ANA by IIFA, ELISA-based methods can be used to:

• Quantitatively measure specific anti-ENA antibodies 1
• Monitor disease activity (particularly anti-dsDNA in SLE using the same method consistently) 1

2. In High Clinical Suspicion Scenarios

Even with negative ANA screening, specific antibody testing should proceed when clinical suspicion is high 1:

• Anti-Jo-1 for suspected inflammatory myopathies
• Anti-ribosomal P for SLE
• Anti-SS-A/Ro for congenital heart block/neonatal lupus/Sjögren's syndrome/subacute cutaneous lupus

This is crucial because certain antibodies (Jo-1, ribosomal P, SS-A/Ro) may be present in patients who are ANA-negative by IIFA 1.

Critical Limitations of ELISA Screening

Research demonstrates significant discrepancies:

• In juvenile idiopathic arthritis (JIA): ELISA showed 21% false-negative rate compared to IIFA, with all false-negatives having significant or high IIFA titers 2
• In SLE: ELISA performed better with 100% consistency with IIFA 2
• ELISA sensitivities range 90-97% vs. 80% for IIFA in SLE, but specificities vary widely (36-94% vs. 99% for IIFA) 3

Recommended Testing Algorithm

1. Initial screening: Use IIFA on HEp-2 cells at 1:160 dilution 1
2. If IIFA positive: Report pattern and titer, then proceed to specific antibody testing based on pattern and clinical context 1
3. If ELISA used and negative but high clinical suspicion: Confirm with IIFA 1
4. For monitoring: Use quantitative ELISA for anti-dsDNA in established SLE, maintaining the same method 1

Common Pitfalls to Avoid

• Never rely solely on ELISA for initial ANA screening - you will miss clinically significant cases, particularly in JIA 2
• Don't order concurrent ANA and subserologies - this violates Choosing Wisely recommendations; only 2.2% of negative ANAs had positive subserologies 4
• Don't skip IIFA confirmation when ELISA is used as initial screen and clinical suspicion remains high 1, 5
• Specify the method used when reporting results, as different platforms have different performance characteristics 1

Quality Considerations

Laboratories using ELISA must:

• Verify recommended cut-offs using local population controls (95th percentile) 1
• Use ROC curve analysis for anti-dsDNA and anti-ENA antibodies 1
• Report the specific method used 1

The bottom line: ELISA may be more cost-effective for high-volume screening 3, 6, but IIFA remains essential for diagnostic accuracy, particularly in conditions like JIA where ELISA demonstrates unacceptable false-negative rates.